The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft propulsion assembly conventionally comprises a turbojet engine housed inside a nacelle.
The nacelle generally has an annular structure comprising an air inlet upstream of the turbojet engine, a median section intended to surround a fan of said turbojet engine and its casing, and a downstream section intended to surround the combustion chamber of the turbojet engine and accommodating if necessary thrust reversal means.
It may be terminated by an ejection nozzle of which the output is located downstream of the turbojet engine.
The air inlet structure is used to optimize the air capture needed to power the fan of the turbojet engine and channel it towards this fan.
An air inlet structure comprises in particular upstream a leading edge structure commonly called air inlet “lip”.
The air inlet lip provides the air capture and is fastened to the rest of the air inlet structure which provides the channeling of the captured air towards the turbojet engine.
To do this, the rest of the air inlet structure has a substantially annular structure comprising an outer panel providing the outer aerodynamic continuity of the nacelle and an inner panel providing the inner aerodynamic continuity of the nacelle, in particular with the fan casing at the median section. The air inlet lip provides the junction between these two walls and may in particular be integrated to the outer panel.
Such nacelles comprising an air inlet lip integrated to the outer panel are called “laminar” and the outer panel/air inlet lip assembly can be movably mounted in translation along a longitudinal direction of the nacelle, in such a manner that it allows the upstream opening thereof. Such a nacelle is described in FR 2 906 568 and EP 2 344 385 documents, for example.
The inner surface of the air inlet structure is exposed to a significant air flow and is located in the vicinity of the blades of the fan. It is therefore located in a significant noise area.
In order to better remedy this situation and in order to reduce the noise pollution generated by the turbojet engine, the inner panel of the air inlet section is equipped with an acoustic attenuation structure.
This acoustic attenuation structure is in the form of a honeycomb core sandwich panel having a perforated outer skin, said acoustic skin, intended to be exposed to noise, and a full inner skin providing in particular the mechanical hold of the panel. The honeycomb core thus constitutes a resonator capable of trapping acoustic waves.
The air inlet lip may also be equipped with an acoustic attenuation structure on an inner portion of the latter.
In the case of a laminar nacelle having an outer mobile cover formed by the outer panel and the air inlet lip, there is a junction at the inner face of the air inlet structure between the inner end of the air inlet lip and the upstream end of the outer panel.
In order to provide the positioning, the centering and the locking of the movable structure on the inner fixed panel in operating position, the air inlet lip and the inner panel are equipped with junction flanges, locking means, seal members, an aerodynamic continuity flap, stoppers, etc. . .
This junction leads to a loss of the available acoustic surface related to the volume required for the implementation of these members, flaps, and stoppers, among others.
More specifically, the stoppers serve as centering device between the lip and the inner panel and are fixed on the panel on the air inlet lip side by means of screws, with an access on the nut side within a C closure. The same assembly principle is used for the aerodynamic flap.
The flange on the lip side is also used as a support for the setting of a peripheral seal member and also serves as a support for the stoppers and the aerodynamic flap. All these functions impact the beginning of the acoustic area on either side of said junction area.
Hence, there is a need for a solution for centering and maintaining such a structure to reduce the junction area not equipped with an acoustic attenuation structure.